A method of manufacturing a semiconductor device includes forming a gate structure through a first insulating interlayer on a substrate such that the gate structure includes a spacer on a sidewall thereof, forming a first hard mask on the gate structure, partially removing the first insulating interlayer using the first hard mask as an etching mask to form a first contact hole such that the first contact hole exposes a top surface of the substrate, forming a metal silicide pattern on the top surface of the substrate exposed by the first contact hole, and forming a plug electrically connected to the metal silicide pattern.